1. Field of the Invention
This invention is in the field of copper recovery by means of a combination of smelting to produce a copper matte and a primary slag, converting the matte into blister copper in a converter which produces a converter slag, and then treating both slags which have relatively high copper contents under reducing conditions to recover additional amounts of copper.
2. Description of the Prior Art
Conventional means for the pyrometallurgical production of copper from sulfidic ores and/or concentrates result in the production of a copper matte and a primary slag by means of a smelting process with suitable additives under approximately neutral or slightly reducing conditions. The matte typically has copper contents on the order of 50% or less, and the primary slag has a copper content usually under 1%. The primary slag is generally discarded, particularly when it is not economical to recover the copper contained therein.
For every metric ton of copper generated, an average of two to three tons of primary slag is produced, and the copper losses per ton of copper produced generally lie in the range of about 10 to 25 kilograms. At a copper price of, for example, $2.00 per kilogram, a possible loss of 25 kilograms per ton represents a cost of $50.00, which is a not inconsiderable sum adding to production costs.
There is approximately a constant relationship between the copper content in the matte and the copper content in the primary slag when using conventional melting methods. According to the publication "Extractive Metallurgy of Copper" by Biswas (Pergamon Press), the copper contents in the two phases correspond to the equation: ##EQU1##
According to the same publication, on page 209, FIG. 10.3, the copper content in the primary slag increases progressively with higher copper contents in the matte and can produce copper contents between 4 and 6% in the primary slag depending on the composition of the initial substances as well as the manner in which the process is carried out. It is possible under these circumstances to produce a matte which is very high in copper, for example, about 80% copper, but for reasons of economics, such a manner of carrying out the process has hitherto been avoided insofar as possible.
In the conversion of the matte into blister copper, the copper content in the converter slag generally reaches magnitudes on the order of up to 15%. It is a matter both of oxidic copper in solution in the slag as well as inclusions of copper matte and inclusions of metallic copper, produced both by the high oxidation potential as well as the violent bath motion occurring during the conversion process.
The prior art used various means for regaining the copper from the converter slag. For example, the copper could be settled in a reducing atmosphere in a settling furnace, generally an electric furnace, with a settling time of a few hours in order to produce a low copper final slag having a copper content about 0.5%. Another method provided for recirculation of the converter slag into the smelting reactor in order to provide the slag with an opportunity to produce sedimentary precipitation of the copper content. Another method consisted in grinding the granulated slag and floating it on the copper. All these methods were relatively complicated and quite expensive.
It is accordingly understandable that in the prior art, an attempt was made to keep the copper content of the primary slag as low as possible in order to reduce the costs due to the loss of copper, thus lowering the production costs. The relatively low copper content resulting in the primary slag and matte corresponding to the equilibrium of the copper contents in the primary slag and matte, being on the order of 30 to 40%, requires a more severe conversion utilizing greater converter volumes, more consumption of reaction agent, larger amounts of converter slags, and correspondingly higher costs.
In view of the relationship of the copper contents of matte and primary slag, and the relationship between smelt, conversion, and slag cleaning costs, the prior art previously only had the choice of shifting the emphasis of the related process steps toward one or the other to a greater or lesser degree depending upon the starting materials, as well as the available apparatus and sources of energy. Such technical compromises, however, were not always satisfactory.